The degree of cross-sectional area (XSA) narrowing by atherosclerotic plaque in each of the 4 major epicardial coronary arteries (right, left main, left anterior descending and left circumflex) was determined at necropsy in 37 patients (30 men and 7 women) aged 34 to 77 years (mean 54) with severe, isolated, chronic, pure aortic regurgitation (AR). In 7 patients (19%), Greater than or Equal to 1 major coronary artery was narrowed 76 to 100% in XSA at some point. Of the 148 major coronary arteries examined in the 37 patients, 12 arteries (8%) were narrowed at some point 76 to 100% in XSA. Each of the 148 major coronary arteries were divided into 5-mm-long segments (average 53 per patient) and a histologic section from each segment was examined. Of the 1,977 segments, 1,087 were narrowed 0 to 25%, 669 (34%) 26 to 50%, 170 (9%) 51 to 75%, 48 (2%) 76 to 95% and 3 (0.001%) 96 to 100%. The average amount of XSA narrowing by atherosclerotic plaque per segment was about 28%. Of the 37 patients, 9 had had angina pectoris, 2 of whom had significant (Greater than 75% XSA reduction) coronary narrowing; 2 other patients had had acute myocardial infarction clinically, 1 of whom had significant coronary narrowing at necropsy. Thus, in general, the amount of coronary narrowing in our 37 adults with severe, pure, isolated, chronic AR was relatively mild.